KR20110078595A - Method of non-destructive test - Google Patents

Abstract

PURPOSE: A nondestructive inspection method is provided to enhance efficiency by performing backward movement through data processing by improving a data processing process. CONSTITUTION: A nondestructive inspection method comprises following steps. After transmitting an initial input signal, response signals are measured at a target poin(S20,S30)t. A corrected response signal is produced by removing of some of the response signals(S40). A corrected transfer function is produced using the corrected response signal and the initial input signal(S50). After time inversion of the corrected response signal, a feedback signal is produced using the time-inversed corrected response signal and the corrected transfer function. The defect of a structure is produced by analyzing of the feedback signal.

Description

Non-destructive testing method {METHOD OF NON-DESTRUCTIVE TEST}

The present invention relates to a non-destructive inspection method, and more particularly, to a non-destructive inspection method for facilitating defect detection by performing a backward process computerized using a correction transfer function.

In general, nondestructive inspection of structures using elastic waves is an important technique in structural design and structure maintenance. Through these nondestructive tests, the aging and damage states of the test object are examined and the mechanical strength of the object is designed to design the optimum structure of the test object.

These nondestructive tests have a long history, and the types of techniques vary. The non-destructive inspection is a method using mostly reference data.

The method using this reference data secures the response signal to the reference input signal before the defect occurs in the structure, and uses the signal difference calculated by comparing the response signal measured when the defect occurs in the structure. To calculate.

Since the method using the reference data can be continuously changed according to the point of time and environment changes obtained by the reference data, many errors occur in the result of the determination of defect occurrence using the reference data.

In order to overcome this problem, a non-destructive testing technique that does not use reference data has been proposed. As a non-destructive testing technique that does not use such reference data, a technique that utilizes the time reversal phenomenon of induced ultrasonic waves is proposed.

Non-destructive testing using the time reversal phenomenon consists of the following process.

Step 1: Forward process of transmitting the initial input signal at the initial point (A point) and then measuring and storing the response signal at the target point (B point)

Step 2: Reverse process that time-reverses the response signal measured at point B, retransmits it as a new input signal at point B, and then measures and stores the feedback signal propagated to point A where the initial input signal was sent.

Step 3: Detecting a defect using an initial input signal and a feedback signal

Thus, the specific defect detection method of the three-step non-destructive inspection is as follows.

When a certain type of input signal is transmitted by using a piezoelectric element (PZT) actuator or the like at a position (point A) of the structure, guided ultrasonic waves are generated inside the structure and propagated to a target point (B point).

The signal propagated to the target point is measured and stored using a piezoelectric material sensor or the like, and the stored signal is reversed in the order of the first and the last signal, which is called time reversal.

When the time-inverted response signal is applied to the structure using a new input signal at point B, the induced ultrasonic waves propagate in the reverse direction to the structure. The guided ultrasonic wave propagated as described above returns to point A, which is the starting position, and measures and stores the response signal returned from point A.

In this case, if there is no coupling inside the structure, the feedback signal measured at point A is compared with the input signal transmitted first at point A, and the shape and characteristics of both signals are the same, and if there is a defect inside the structure, Due to the reflected wave generated by the defect, the shape and characteristics of both signals are different.

Conventional non-destructive inspection methods using time reversal detect such defects using such characteristics.

However, since the non-destructive inspection method using the time reversal performs the backward process in practice, there is a problem in that an algorithm and an apparatus for time reversing the response signal and synchronizing and retransmitting several time-reversed signals are additionally required. It is disadvantageous in that economic efficiency is low and a large device space and working time are required.

In addition, there is a problem that it is difficult to process a signal for detecting a defect because an excessive number of lamb wave modes are generated in the feedback signal, and defects are detected by simply comparing the initial input signal with the feedback signal, and thus, due to dispersion and multi-mode characteristics of the induced ultrasonic wave. A problem arises in that a detection error occurs due to a difference in both signals generated.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and is to provide a non-destructive inspection method that improves data processing and improves efficiency and economics by performing a backward process by a computer technique.

In order to achieve the above object, the present invention includes the steps of measuring the response signal of the target point after the initial input signal transmission; Calculating a correction response signal by removing a part of the signal from the response signal; Calculating a correction transfer function using the correction response signal and the initial input signal; Calculating a feedback signal by time-inverting the correction response signal and using the time-inverted correction response signal and the correction transfer function; It provides a non-destructive inspection method comprising; calculating a defect of the structure by analyzing the feedback signal.

는

로 정의되고, 상기 귀환신호

는

이다. Preferably, the initial input signal is a lamb wave signal, the response signal is classified into an S wave and an A wave, and the correction response signal is a signal excluding the S wave from the response signal, and the correction transfer function

Is

Defined by the feedback signal

Is

to be.

The calculating of the defect of the structure may include selecting a time reference point of a feedback signal; Calculating a non-time for a defect signal among feedback signals with respect to the time reference; Imaging the defect using the non-time, wherein the time reference point of the feedback signal is a left-right symmetry point of the feedback signal.

According to the present invention described above, the actual measurement process is performed only in the forward process, and the reverse process removes some waveforms relatively unrelated to the defect, and then performs the time inversion process to simplify the signal processing for defect detection by simplifying the feedback signal. In addition, by using this method, the backward process of the non-destructive testing method can be performed by the computational method to increase the efficiency and economic efficiency of the non-destructive testing method.

The beamforming technique is applied to the feedback signal to image the position and shape of the defect, and at the same time, the position of each sensor is also represented as an image so that the position of the defect can be detected more accurately.

Hereinafter, with reference to the accompanying drawings looks at in detail with respect to the non-destructive testing method according to an embodiment of the present invention.

2 is a test flow chart of a non-destructive test according to an embodiment of the present invention, Figure 3 is a conceptual diagram of a non-destructive test according to an embodiment of the present invention, Figure 4 is a test result for the mutual theory of lamb wave, Figure 5 is an experimental result of the time reversal process of the non-destructive test according to the comparative example, Figure 6 is a calculation result of the feedback signal for the non-destructive test according to an embodiment of the present invention, Figure 7 is an embodiment of the present invention FIG. 8 is a schematic diagram showing the propagation distance of the lamb wave for calculating the non-destructive time of the non-destructive test according to an embodiment of the present invention, and FIG. An image of the joint detection result, and FIG. 10 is a graph showing an envelope of the feedback signal.

The terms or words used in this specification and claims are not to be construed as limiting in their usual or dictionary meanings, and the inventors may appropriately define the concept of terms in order to best explain their invention in the best way possible. It should be interpreted as meaning and concept corresponding to the technical idea of the present invention based on the principle that the present invention.

Therefore, the embodiments described in the specification and the drawings shown in the drawings are only one of the most preferred embodiments of the present invention, and do not represent all of the technical idea of the present invention, these can be replaced at the time of the present application It should be understood that there may be various equivalents and variations.

2, the non-destructive inspection method according to an embodiment of the present invention, the input signal transmission and response signal measuring step (S10), the step of calculating the correction response signal (S20), the step of calculating the correction transfer function (S30) , The time inversion signal calculation and transmission step (S40), the feedback signal calculation step (S50) and the step of calculating the defect (S60).

In the response signal measuring step S10, the input signal 10 V _A is transmitted at an initial point (A point) and the response signal 20 V _B is measured at the destination point (B point). The input signal 10 can be used as long as it is a narrowband signal including a tone-burst signal, a chirp signal, and the like. In this embodiment, a lamb wave is used.

When the lamb wave is applied to the input signal 10, the response signal 20 at point B is measured, and as shown in FIG. 3, according to the center frequency of the input signal 10 and the frequency band of the spectrum. The response signal 20 is composed of two or more components. Since each component propagates at different speeds and magnitudes, the response signal 20 measured at an arbitrary position has a significantly different complicated pattern compared to the input signal 10.

Therefore, in this embodiment, the center frequency of the input signal 10 is limited to about 500 Hz or less so that the response signal component induced in the structure is limited to two S components 21 and A components 22, and the magnitude of the A component is S. Tune the center frequency so that it is much larger than the size of the components.

In this tuned state, when the response signal of the comparative example for comparison with the present embodiment is measured and measured, time reversal obtained by time reversing the response signal V _{B and} the response signal V _B measured at the input signals V _{A and} B The feedback signal V _A ^TR measured at the signal V _B ^* and the A point is measured as shown in FIG. 5.

The response signal V _B is the S component and the A component of the response signal propagated as it is along the straight path AB, and the S component of the lamb wave is propagated toward the defect and is reflected from the defect. Signal reached (marked SS in the figure) and component converted to point B in the form of component A (marked SA in the drawing), and similarly component A propagated toward the defect and reflected there, then point B It consists of two signals propagated into (indicated by AS and AA in the figure).

에는 도 5의 마지막 그림에 도시한 바와 같이 몇몇 신호 성분만이 지배적으로 측정된다. 도 5에 표시된 신호성분 중 A/S는 직선경로 A-B를 따라 B점으로 입사된 A 성분이 S 성분으로 변환된 후 변환된 S 성분이 직선 경로 B-A를 따라서 A점에 전파된 신호 성분을 나타내며, A/AA는 직선경로 A-B를 따라 B점에서 입사된 A 성분이 동일한 성분형태로 결함 쪽으로 향한 후 그 곳에서 반사되어 동일한 A 성분 형태로 A점에 전파된 것을 의미한다. 다른 기호에 대해서도 동일한 방법으로 설명된다.In the comparative example of this embodiment, the center frequency of the input signal is tuned such that the magnitude of the A component is much larger than that of the S component, so that the magnitudes of the signal components AS, SA, and SS are actually very small compared to other signal components. . Signal components AS, SA, and SS are mostly reduced in size during time reversal, so the feedback signal

In Fig. 5, only some signal components are dominantly measured, as shown in the last figure of FIG. Among the signal components shown in FIG. 5, A / S represents a signal component propagated at point A along the straight path BA after the converted A component is converted to the S component after the A component incident at the point B along the straight path AB is converted into the S component. A / AA means that the A component incident at point B along the straight path AB is directed toward the defect in the same component form and then reflected there and propagated to the point A in the form of the same A component. Other symbols are described in the same way.

Referring to the feedback signal of FIG. 5, it can be seen that only signal components AA / AA, AA / S, and A / AA have information about the defect as a signal returned through the defect.

That is, as can be seen in the comparative example, the feedback signal includes components having information on defects, but signal components (A / S and S / A) having no information on defects are included. It can be seen that the component analysis is complicated.

In order to solve this problem, the non-destructive inspection method according to an embodiment of the present invention simplifies the feedback signal by removing a signal having no information on a defect in advance, and then calculates a feedback signal using a corrected transfer function. do.

(30), 시간반전된 보정응답신호

(40) 및 귀환신호

(50)이다. 6 is an input signal V _A 10, a correction response signal calculated by a non-destructive inspection method according to an embodiment of the present invention.

30, time inverted correction response signal

40 and return signal

50.

를 이용하여 보정전달함수

를 산출한다.(S30)In the non-destructive testing method according to an embodiment of the present invention, after removing the signal component (S component) that arrives the earliest from the response signal measured at point B, the corrected response signal from which the S component is removed

Correction transfer function using

Calculate (S30).

The correction transfer function is determined by the following equation.

The transfer function G _AB (ω), which is input from point A by the reciprocal theorem of the structure and calculated as the response measured at point B, is calculated from the response measured at point A, which is input from point B. Same as _BA (ω). That is, G _AB (ω) = G _BA (ω) = G (ω).

이므로, 보정전달함수는 수학식 1과 같이 초기입력신호 및 보정응답신호에 의하여 정하여 진다. Therefore, the correction transfer function

Therefore, the correction transfer function is determined by the initial input signal and the correction response signal as shown in Equation (1).

When the correction transfer function is determined in Equation 1, after time-inverting the correction response signal (S40), a feedback signal is calculated using the time-inverted correction response signal and the correction transfer function (S50).

The feedback signal is calculated by Equation 2.

Referring to FIG. 6, only the signal components AA / A and A / AA having information on defects on the left and right are centered on the signal components A / A and AA / AA. In the present embodiment illustrated in FIG. 6, the signal components A / S and S / A are excluded, but other forms of unnecessary signal components other than the signal components A / S and S / A may be removed.

When the feedback signal is calculated, the feedback signal is analyzed next to calculate a defect of the structure.

Computing the defect of the structure (S60), the step of selecting a time reference point of the feedback signal (S61); Calculating a non-time for a defect signal among feedback signals with respect to the time reference (S62); In operation S63, the defect is imaged using the non-time.

Defect calculation step (S60) of the structure is to use the imaging technique of detecting a defect by measuring the time of flight (TOF) of the components of the feedback signal, and then image it using it.

Referring to FIG. 7, a time reference point S61 of a feedback signal is selected to measure a specific time of each component of the feedback signal. The time reference point 60 is calculated by setting the left and right symmetry points of the feedback signal 50.

)와의 차이의 크기 순서에 따라 k번째 결함에 의해 생성된 신호 성분 A/AA^{( k )}와 AA^{( k )}/A가 귀환신호의 좌우 대칭점을 중심으로 좌우 위치에 배치된다. If two or more defects exist, the distances d _AB and A, k of a straight path connecting point A (input signal application point) and point B (response signal detection point) as shown in Figs. First defect D ^{( k )} , the distance of the bypass

The signal components A / AA ^{( k )} and AA ^{( k )} / A generated by the k th defect are arranged in the left and right positions around the left and right symmetry points of the feedback signal according to the magnitude order of the difference from the?

The distance between the non-time and the detour path of these signals has a relationship of the following equation.

Where v is the propagation velocity of the lamb wave. Substituting a numerical value of R ^(k) for an arbitrary pixel into Equation 3 above to find the non-time for the pixel, and find the waveform value of the feedback signal corresponding to the non-time calculated in FIG. When the waveform value of the feedback signal is imaged on a plane, pixels corresponding to the trajectory of the ellipse are implemented as the same image. If a plurality of initial points (input signal application points) and target points (response signal detection points) are selected and the calculation process of this embodiment is repeated, a plurality of elliptic trajectories are formed and colors are applied to the overlapping pixels. When the display is divided, the defect is imaged and detected as shown in FIG. 9.

In more detail, the imaging process is as follows.

First, an image processing feedback signal calculated from the data of FIG. 7 for the ij-th propagation path determined by an arbitrary i-th input signal application point and a j-th response signal detection point is called S _ij (t). . In the case of calculating the image processing feedback signal from the data of FIG. 7, a method of directly calculating the data using the data of FIG. 7 may be used. However, the data of FIG. 7 may be processed into an envelope form of FIG. Can be calculated.

The time taken for the ram wave to propagate to a pixel at an arbitrary position (x, y) corresponds to the non-time of Equation 3. The non-time is a function of pixel position (x, y). The value of the feedback signal at the non-time TOF (x, y) corresponding to the position (x, y) of the pixel, that is, S _ij (t) = S _ij (x, y) at t = TOF (x, y) Using the value, the image value I (x, y) (or RGB level) for the corresponding pixel is determined by Equation 4 or Equation 5 illustrated below.

or,

이다. 위 식에서 N은 사용된 액츄에이터와 센서의 수(입력신호인가점 및 응답신호 검출점의 수)이고, 지수 p는 일반적으로 2 이상의 정수 값으로 선택하여 결함의 위치 정보를 보다 강하게 이미지화 한다. 본 실시예에서는 상기 수학식 4 또는 수학식 5를 이용하였으나, 본 실시예의 이미지 값을 결정하는 수식 이외에 이를 변형한 다른 가능한 수식과 방법도 본 발명의 이미지화 과정에 사용할 수 있다. here,

to be. In the above formula, N is the number of actuators and sensors used (the number of input signal application points and response signal detection points), and the index p is generally selected as an integer value of 2 or more to image the position information of the defect more strongly. Although Equation 4 or Equation 5 is used in the present embodiment, in addition to the equation for determining the image value of the present embodiment, other possible equations and methods may be used in the imaging process of the present invention.

When imaged using the image value I (x, y) for each pixel detected as described above, defects may be imaged and represented as shown in FIG. 9.

As mentioned above, although this invention was demonstrated by the limited embodiment and drawing, this invention is not limited by this, The person of ordinary skill in the art to which this invention belongs, Of course, various modifications and variations are possible within the scope of equivalent claims.

1 is a conceptual diagram of a non-destructive inspection according to the prior art.

2 is a test flowchart of a non-destructive test according to an embodiment of the present invention.

3 is a conceptual diagram of a non-destructive test according to an embodiment of the present invention.

4 is a test result for the mutual theory of lamb wave.

5 is an experimental result of the time reversal process of the non-destructive test according to the comparative example.

6 is a result of calculating the feedback signal for the non-destructive test according to an embodiment of the present invention.

7 is an experimental result showing the time period of the feedback signal of the non-destructive test according to an embodiment of the present invention.

8 is a schematic diagram showing a propagation distance of a lamb wave for calculating a non-destructive time of a non-destructive test according to an embodiment of the present invention.

9 is an image of a combined detection result imaged by non-destructive testing according to an embodiment of the present invention.

10 is a graph showing an envelope of a feedback signal.

<Brief description of symbols for the main parts of the drawings>

10: input signal 20: response signal

30: correction response signal 40: time reversal signal

50: return signal 60: time reference point

61: non-time

Claims (9)

Measuring the response signal of the target point after transmitting the initial input signal; Calculating a correction response signal by removing a part of the signal from the response signal; Calculating a correction transfer function using the correction response signal and the initial input signal; Calculating a feedback signal by time-inverting the correction response signal and using the time-inverted correction response signal and the correction transfer function; A non-destructive inspection method comprising: calculating a defect of the structure by analyzing the feedback signal; The method according to claim 1, And the initial input signal is a lamb wave signal, the response signal is classified into an S wave and an A wave, and the correction response signal is a signal excluding the S wave from the response signal. The method according to claim 1, And the initial input signal is a RAM wave signal, the response signal is classified into an S wave and an A wave, and the correction response signal is a signal excluding the A wave from the response signal. The method according to claim 1, The correction transfer function

Is a non-destructive testing method determined by the following equation (1). [Equation 1]

V _B The method according to claim 1, The feedback signal is a non-destructive testing method calculated by the following equation (2). [Equation 2]

The method according to claim 1, Computing the defect of the structure, Selecting a time reference point of the feedback signal; Calculating a non-time for a defect signal among feedback signals with respect to the time reference; Nondestructive inspection method comprising the step of imaging the defect using the non-time. The method according to claim 6, The time reference point of the feedback signal is a non-destructive inspection method of the left and right symmetry of the feedback signal. The method according to claim 6, Imaging the bond, Calculating a feedback signal S _ij (t) for image processing using the following equation 3 for the distance R ^(k) of the bypass path and the distance TOF ^(k) of the defect signal; And calculating an image value ( I ( x, y )) for a pixel at an arbitrary position by using Equation 4 from the calculated image processing feedback signal. &Quot; (3) &quot;

here,

ν: speed of lamb wave d _AB : Distance between point A and B &Quot; (4) &quot;

The method according to claim 6, Imaging the bond, Calculating a feedback signal S _ij (t) for image processing using the following equation 3 for the distance R ^(k) of the bypass path and the distance TOF ^(k) of the defect signal; And calculating an image value ( I ( x, y )) for a pixel at an arbitrary position by using Equation 5 from the calculated image processing feedback signal. [Equation 5]

here,

to be.

Images